fix multipart mime update issue when msg is not generated by email
fix multipart mime update issue when msg is not generated by email

The multipart mime update against an object may send a request with
message generated not using the email library in this case, the
request body does not include the content type and boundary. thus
the message is considered as a bulk of stream. That is why it fails
getting the content for the object.

osaddon/cdmi,osaddon/cdmi